Es wird eine Technologie für die Aktivierung von gepreßten Pulver-Materialien (bis 500 mg) in einem Protonenstrom (10 µA) beschrieben. Das Verfahren wurde für die Herstellung von 94mTc am Rossendorfer Zyklotron U-120 aus angereichertem 94MoO3-Pulver optimiert. Die Bestrahlung des gepreßten Targetmaterials erfolgt in einem evakuierten und drucküberwachten Targetträger mit dünnem Strahleintrittsfenster. Durch die gute Wärmekopplung des Preßlings mit dem wassergekühlten Targetträger und der heli-umgekühlten Fensterfolie kann das Targetmaterial mit einer absorbierten Strahllei-stung bis zu 40 W belastet werden. Bei einem Folienbruch verhindert der geschlosse-ne Heliumkreislauf das Entweichen von radioaktivem Material. Zur Reduktion der Energieabsorption im Target wird die Dicke des Targetmaterials der Wirkungsquer-schnittsverteilung angepaßt. Nach der Entnahme des Targetträgers aus der Bestrah-lungsanlage verbleibt das Targetmaterial bis zur Aufarbeitung in einem radiochemi-schen Labor in dem geschlossenen Targetträger. The technology described has been developed for safe activation of pressed powder materials (up to 500 mg) in a proton beam (10 µA). The procedure has been optimized for the production of 94mTc with the Rossendorf U-120 cyclotron using enriched 94MoO3. The target material is irradiated inside an evacuated and pressure controlled tar-getholder equipped with a thin entrance window for the proton beam. The target with-stands an absorbed beam power of about 40 W as the result of a good heat coupling between the target material and the water-cooled target holder as well as the helium-cooled entrance window. In the case of a window break the closed helium circuit pre-vents the escape of radioactivity. To diminish the energy absorption in the target the thickness is adapted to the distribution of the cross section. After taking the target holder out of the irradiation equipment, the target remains closed in the target holder …

Das Rossendorfer Zyklotron ist ein \"klassisches\" Zyklotron mit 120 cm Polschuhdurchmesser. Als klassisches Zyklotron verfügt es über ein rotationssymmetrisches Magnetfeld. Mit der in radialer Richtung abfallenden Magnetfeldstärke wir die \"weiche\" Fokussierung erreicht. Zunächst wurde das zyklotron für die kernphysikalische Grundlagenforschung genutzt. Später überwogen die Herstellung von Radionukliden, die Neutronenerzeugung für medizinische und radiochemische Anwendungen sowie spezielle Dünnschichtaktivierungen für die Verschleißforschung. Die Betriebszeit des Zyklotrons erstreckte sich über einen zeitraum von 41 Jahren, von August 1958 bis Dezember 1999.

Das Rossendorfer Zyklotron ist ein \"klassisches\" Zyklotron mit 120 cm Polschuhdurchmesser. Als klassisches Zyklotron verfügt es über ein rotationssymmetrisches Magnetfeld. Mit der in radialer Richtung abfallenden Magnetfeldstärke wir die \"weiche\" Fokussierung erreicht. Zunächst wurde das zyklotron für die kernphysikalische Grundlagenforschung genutzt. Später überwogen die Herstellung von Radionukliden, die Neutronenerzeugung für medizinische und radiochemische Anwendungen sowie spezielle Dünnschichtaktivierungen für die Verschleißforschung. Die Betriebszeit des Zyklotrons erstreckte sich über einen zeitraum von 41 Jahren, von August 1958 bis Dezember 1999.

Introduction When properly maintained, cyclotrons often remain in operation for 20 years and more. However, as the years pass the control systems in particular become challenging to support. The I/O cards and other hardware eventually become obsolete, making spare parts difficult or even impossible to find. And the knowledge and ability to reload and configure the software also gets lost as operating systems and media storage technology change. This obsolescence is true of the Siemens RDS-112 cyclotron, which is controlled using a 486 computer, connected to an external STD card rack containing up to 15 I/O cards. These I/O cards were last manufactured in the 1990’s, and the iRMX-based control programs malfunction on computers newer than a 486 processor. A control system upgrade for the RDS-112 cyclotron has been developed by PET Technical Consulting Inc. This commercially available control system reduces operator training time, requires less maintenance, and supports new targets and custom product processes. Material and Methods The availability of high channel count I/O cards, and the decision not to support the old CPCU synthesis units, means the entire STD card rack can be replaced with 5 National Instruments (NI) I/O cards. The replacement computer is an industrial grade rack mounted PC with RAID 1 mirrored pair hard drives in front panel access quick swap bays. Two NI PCI-6509 Digital I/O cards connect directly to the RDS electronics, channel assignments are mapped using software configuration. Three NI PCI-6229 Multifunction I/O cards connect to the RDS electronics through a cable breakout interface plate, the terminal blocks are wired as needed to map the channels. The new control software was created using National Instruments LabVIEW. The new control sequences have a core based on the original RDS-112 FORTRAN control programs. Then hundreds of improvements were made to simplify operation, increase flexibility, minimize user involvement and mistakes, and clearly display key parameters and fault conditions. System control has been combined into a comprehensive Graphical User Interface, with controls and indicators grouped together onto subsystem pages. Commands that once needed to be typed-in have been replaced with a clickable control for each function. Bar graphs display target and slit currents. Status is obvious with red faults against normally green indicators. Audio alarms cue the operator for process interaction, warn if target current or pressure drifts from setpoint, or if faults occur with power supplies, vacuum, or water cooling. Improvements in sequences and beam algorithms have reduced the time to achieve full beam on dual targets from 10 minutes down to 3 minutes. Results and Conclusion This new control system has been installed on (5) five RDS-112 cyclotrons used for commercial isotope distribution. The total combined operation time of these systems after receiving the upgrade is now over 17 years, during this time the control system operation has been nearly problem free. UPDATE: The Siemens RDS-111 cyclotron is controlled by a VME computer that is now end-of-life. The VM30 and VM42 CPU boards and many of the I/O modules are no longer manu-factured. PET Technical Consulting is developing a control system replacement for the RDS-111 cyclotron with expected completion in 2014.

Introduction Measuring the beam profile on a medical cyclo-tron in real time can aid in improved tuning of the cyclotron and give important information for a smooth operation. Typically the beam profile is measured by an autoradiography technique or even by a scintillator that can be viewed in real time [1, 2]. Another method is to use collimators in front of the target to assess the beam center-ing [3]. All these methods have potential draw-backs including; an inability to monitor the beam in real time for the radiograph, exhibiting a non-linear correlation in signal response to the power deposited for a scintillator, and not providing a 2-dimensional profile of the complete beam for collimators. Our goal was to design a realtime, linear, 2-dimensional beam-profile monitor that is able to withstand the high power of a PET cyclotron. Material and Methods The beam-profile monitor (PM) is designed for the TR13, a 13MeV negative hydrogen-ion cyclotron at TRIUMF. The design follows the concept of a ‘harp’ monitor, widely used at TRIUMF for tuning proton and radioactive ion beams, and is installed on the extraction port without separation from the tank vacuum. The TR13 monitor is designed to withstand a 13 MeV proton beam with a beam current of up to 25 µA, has an active area of 10 by 10 mm and does not affect the 10-7 torr tank vacuum. The device consists of a water-cooled Faraday cup made out of aluminium for low activation and two orthogonal rows of eight tungsten electrodes each mounted on a water-cooled support frame. Electrodes are spaced 1 mm apart from each other, see FIG. 1. The electrodes are electrically isolated from each other and each has a current pickup soldered to it. The material and the shape of the electrodes are optimized to withstand the deposited power of the proton beam. A voltage of -90 V is applied to the electrodes to repel secondary electrons and prevent crosstalk between neighbouring electrodes. The electrode current is amplified using a custom current amplifier, and read by an ADC. From there, the current data is displayed on a PC. This allows one to observe changes of the beam profile in real time. The electronics are designed to read out all sixteen channels in parallel, or, if only a limited number of ADC channels are available, to cycle through the different channels. In our current setup all sixteen channels are read out simultaneously. Results and Conclusion The beam-profile monitor provides a real-time representation of the proton beam, see FIG. 2. The data can also be recorded and analyzed at a later time. The linearity of the monitor has been measured up to 30 µA of proton beam current [4]. With the use of the monitor, it was possible to increase the output of the ion source into the target by 50% in comparison to the standard tune.

Introduction Technetium-99m, the daughter of 99Mo is the most commonly used radioisotope in nuclear medicine [1–2]. Current global crisis of 99Mo supply, aging of nuclear reactors and staggering costs force the search for alternative sources of 99mTc. Radioisotope Centre POLATOM joined the IAEA Coordinated Research Project on “Accelerator-based Alternatives to Non-HEU Production of 99Mo/99mTc”. The planned outcome of this project is development of 99mTc production method using the reaction of 100Mo(p,2n)99mTc [3] in Polish cyclotron. This work presents the results concerning preparation of 100Mo target for irradiation with protons. Material and Methods The manufacturing of Mo target was performed using pressing of molybdenum powder into pellets and its sintering in hydrogen atmosphere at 1600 oC [4]. For this purpose a tantalum and stainless steel plates were used as support. Several pellets using molybdenum powder with particles size of 2 µm in diameter were pressed at different values of pressure. Results and Conclusion The optimized parameters of pressing molyb-denum pellets with various sizes are given in TABLE 1. It was found that the pellets did not adhere neither to the tantalum nor stainless steel plates but they conducted electricity very well. Pellets prepared with higher pressure were more mechanically resistant, however application, even the highest used pressure did not ensure its satisfactory stability. In order to improve mechanical strength, pressed Mo pellets were sintered in hydrogen atmosphere at temperature of 1600 °C. As a result of this process dimensions of Mo pellets decreased: diameter by 13 %, thickness by 12 %, weight by 1.5 %, volume by 34 % while density increased by 50 %. The changes of these parameters are associated with reduction of molybdenum oxide and removal of oxygen from intermetallic space. It was confirmed by photos of microscopic cross section of pellets before and after sintering. It was observed, that after sintering Mo pellets got a metallic form with very high hardness and mechanical strength.

Introduction It is shown that a very simple model reproduces the pressure versus beam current characteristics of elongated single-cavity boiling water targets for 18F production surprisingly well. By fitting the model calculations to measured data, values for a single free parameter, namely an overall heat-transfer coefficient, have been extracted for several IBA Nirta H218O targets. IBA recently released details on their new Nirta targets that have a conical shape, which constitutes an improvement over the original Nirta targets that have a cylindrical shape [1,2]. These shapes are shown schematically in FIGURE 1. A study by Alvord et al. [3] pointed out that elevated pressures and temperatures in excess of the saturation conditions may exist in a water target during bombardment. However, as long as the rate of condensation matches the rate of vaporization, the bulk of the system should remain at saturation conditions. Superheated regions are therefore likely to form but also likely to disappear rapidly, typically on the scale of a few milliseconds. Even though the boiling process is generally quite complex, enhanced by radiation-induced nucleation, the presence of fast mixing mechanisms in the water volume justifies some simplifications to be made. Materials and Methods The simplified model assumes that the bulk of the target water has a constant temperature, which is the same as the inner wall temperature of the cavity, Tw. A second simplification is to neglect the temperature difference across the target chamber wall, which is only justified if the wall is thin. The boiling is not explicitly taken into consideration, including the rather complex boiling behaviour at the Havar window, except to acknowledge that it is the main mixing mechanism. Large temperature gradients can briefly exist in the water medium but they also rapidly disappear. A further assumption is that a single, overall convective heat-transfer coefficient can be applied, which is constant over the entire water-cooled surface. As the wall thickness is neglected, the heat-transfer surface is assumed to be the inner surface of the cavity, excluding the surface of the Havar window. One can then write down an energy balance between the beam heating and the convection cooling (Newton’s law of cooling), where Ib is the beam intensity, ΔE is the energy windows of the target (taken as 18 MeV), h is the convective heat-transfer coefficient, A is the inner cavity surface through which the heat has to be transferred from the target-water volume to the cooling water, and T0 is the cooling-water temperature. The saturated vapour pressure of water versus temperature is a characteristic curve, given by the steam tables [4]. Assuming the bulk of the system at saturation conditions, one gets from (1) and (2). The function f is represented by a polynomial. The only unknown in Equation (3) is the overall convective heat-transfer coefficient h. Our approach was to adjust h until a good fit with a set of measured data was obtained. It also has to be mentioned that subtle differences in the physical properties between 18O-water and natural water have been neglected. All in all, quite a few assumptions and simplifications are made in deriving Equation (3) and the system is, admittedly, much more complex. Nevertheless, the results obtained by applying Equation (3) are rather interesting. Results and Conclusion Measured data and corresponding calculations are shown in FIGURE 2 for three different conical targets and one cylindrical target. The extracted convective heat-transfer coefficients are pre-sented in TABLE 1 for the four cavities. As can be seen in FIGURE 2, while there are some differences between the data and calculated curves, especially towards lower beam currents, the overall agreement is remarkably good. It is possible that the better agreement towards higher beam intensities is related to more ebullient boiling and more rapid mixing, i.e. closer to the conditions that the model assumes. The values obtained for the overall convective heat-transfer coefficient are also remarkably similar. This tells us that, by and large, all the cavities perform in a similar way and the performance in terms of maximum operational beam current depends largely on the available surface to effectively remove the heat from. The values of h increase marginally if a smaller value is adopted for the cooling water. Note that the choice of T0 = 30 ᵒC used to obtain the results in TABLE 1 is typical for the room temperature closed-loop cooling system used at iThemba LABS, once it has stabilized under operational conditions. A study by Buckley [5] on a quite different target design reports a value of h = 0.49 W cm−2 ᵒC−1, which is reassuringly similar. That study describes a cylindrical target cavity with a volume of 0.9 cm3, 8 mm deep, cooled with 25 ᵒC water from the back, operated with a 15 MeV proton beam with an intensity of 30 µA. The Nb Nirta targets are typically filled with 18O-water to about 60% of the cavity volume (see refs. [1,2] for the recommended values). The elongated shape, in combination with the ebullient properties of the boiling water, prevents burn-through. All the targets deliver the expected saturation yield. The targets are self-regulating ─ no external gas pressure is required. While the thermosyphon targets seemingly take advantage of a superior concept, we are now questioning whether this is really so in practice? It is not clear to us that the much more complex thermosyphon targets deliver any operational and/or performance advantages compared to the simple elegance of these elongated, single-cavity boiling target designs.

Cyclotron production of 99mTc through the 100Mo(p,2n)99mTc reaction1 is being actively investigated as an alternative to reactor-based approaches. A challenge facing cyclotron pro-duction of clinical-quality 99mTc is that proton bombardment of Mo targets results in production of a number of additional Tc and non-Tc isotopes through various reaction channels.2,3 While non-Tc products can be chemically re-moved, other Tc radioisotopes cannot and will therefore degrade radionuclidic purity and contribute to patient radiation dose.5 The radionuclidic purity of cyclotron-produced 99mTc depends on the nuclear cross section governing each reaction channel, the proton current and energy distribution, duration of bombardment, target thickness and isotopic composition. Although conditions that minimize dose from radioactive Tc impurities have been identified,5 cyclotron performance and thus irradiation conditions may randomly fluctuate between and/or during production runs. Fluctuations of certain parameters, for example the total number of bombarding protons, are expected to have little influence on radionuclidic purity, whereas fluctuations in beam energy, target thickness and isotopic composition may dramatically affect the relative amounts of 93gTc, 94gTc, 95gTc, and 96gTc impurities. It is critical to quantify relationships between potential fluctuations and the reproducibility and consistency of the radionuclidic purity of cyclotron-produced 99mTc to guide development and optimization of target preparation, irradiation, and processing techniques. The purpose of this work is to present a mathematical formalism for quantifying the relation-ship between random fluctuations in Mo target thickness and variability of proton-induced nuclear reaction rates for enriched Mo targets. In this study, we use 96gTc as an example of impurity which can potentially contribute to increased patient dose for patients injected with cyclotron-produced 99mTc.4 Herein, we apply the developed formalism to both the 96Mo(p,n)96gTc and the 100Mo(p,2n)99mTc reaction channels, however, the same approach can be applied to any reaction channel of interest.

Introduction Technetium-99m, supplied in the form of 99Mo/99mTc generators, is the most widely used radioisotope for nuclear medical imaging. The parent isotope 99Mo is currently produced in nuclear reactors. Recent disruptions in the 99Mo supply chain [1] prompted the development of methods for the direct accelerator-based production of 99mTc. Our approach involves the 100Mo(p,2n)99mTc reaction on isotopically enriched molybdenum using small medical cyclotrons (Ep ≤ 20 MeV), which is a viable method for the production of clinically useful quantities of 99mTc [2]. Multi-Curie production of 99mTc requires a 100Mo target capable of dissipating high beam intensities [3]. We have reported the fabrication of 100Mo targets of both small and large area tar-gets by electrophoretic deposition and subsequent sintering [4]. As part of our efforts to further enhance the performance of molybdenum targets at high beam currents, we have developed a novel target system (initially de-signed for the GE PETtrace cyclotron) based on a pressed and sintered 100Mo plate brazed onto a dispersion-strengthened copper backing. Materials and Methods In the first step, a molybdenum plate is produced similarly to the method described in [5] by compacting approximately 1.5 g of commercially available 100Mo powder using a cylindrical tool of 20 mm diameter. A pressure between 25 kN/cm2 and 250 kN/cm2 is applied by means of a hydraulic press. The pressed molybdenum plate is then sintered in a reducing atmosphere (Ar/2% H2) at 1,700 oC for five hours. The resulting 100Mo plates have about 90–95 % of the molybdenum bulk density. The 100Mo plate is furnace brazed at ~750 oC onto a backing manufactured from a disperse on strengthened copper composite (e.g. Glidcop AL-15) using a high temperature silver-copper brazing filler. This process yields a unique, mechanically and thermally robust target system for high beam power irradiation. Irradiations were performed on the GE PETtrace cyclotrons at LHRI and CPDC with 16.5 MeV protons and beam currents ≥ 100 µA. Targets were visually inspected after a 6 hour, 130 µA bombardment (2.73 kW/cm2, average) and were found fully intact. Up to 4.7 Ci of 99mTc have been produced to date. The saturated production yield remained constant between 2 hour and 6 hour irradiations. Results and Conclusion These results demonstrate that our brazed tar-get assembly can withstand high beam intensities for long irradiations without deterioration. Efforts are currently underway to determine maximum performance parameters.

Introduction The goal of this work is to advance the production and use of 52Mn (t½ = 5.6 d, β+: 242 keV, 29.6%) as a radioisotope for in vivo preclinical nuclear imaging. More specifically, the aims of this study were: (1) to measure the excitation function for the natCr(p,n)52Mn reaction at low energies to verify past results [1–4]; (2) to measure binding constants of Mn(II) to aid the design of a method for isolation of Mn from an irradiated Cr target via ion-exchange chromatography, building upon previously published methods [1,2,5–7]; and (3) to perform phantom imaging by positron emission tomography/magnetic resonance (PET/MR) imaging with 52Mn and non-radioactive Mn(II), since Mn has potential dual-modality benefits that are beginning to be investigated [8]. Material and Methods Thin foils of Cr metal are not available commercially, so we fabricated these in a manner similar to that reported by Tanaka and Furukawa [9]. natCr was electroplated onto Cu discs in an industrial-scale electroplating bath, and then the Cu backing was digested by nitric acid (HNO3). The remaining thin Cr discs (~1 cm diameter) were weighed to determine their thickness (~ 75–85 μm) and arranged into stacked foil targets, along with ~25 μm thick Cu monitor foils. These targets were bombarded with ~15 MeV protons for 1–2 min at ~1–2 μA from a CS-15 cyclotron (The Cyclotron Corporation, Berkeley, CA, USA). The beamline was perpendicular to the foils, which were held in a machined 6061-T6 aluminum alloy target holder. The target holder was mounted in a solid target station with front cooling by a jet of He gas and rear cooling by circulating chilled water (T ≈ 2–5 °C). Following bombardment, these targets were disassembled and the radioisotope products in each foil were counted using a high-purity Ge (HPGe) detector. Cross-sections were calculated for the natCr(p,n)52Mn reaction. Binding constants of Mn(II) were measured by incubating 54Mn(II) (t½ = 312 d) dichloride with anion- or cation-exchange resin (AG 1-X8 (Cl− form) or AG 50W-X8 (H+ form), respectively; both: 200–400 mesh; Bio-Rad, Hercules, CA) in hydrochloric acid (HCl) ranging from 10 mM-8 M (anion-exchange) and from 1 mM-1 M (cation-exchange) or in sulfuric acid (H2SO4) ranging from 10 mM-8 M on cation-exchange resin only. The amount of unbound 54Mn(II) was measured using a gamma counter, and binding constants (KD) were calculated for the various concentrations on both types of ion-exchange resin. We have used the unseparated product for preliminary PET and PET/MR imaging. natCr metal was bombarded and then digested in HCl, resulting in a solution of Cr(III)Cl3 and 52Mn(II)Cl2. This solution was diluted and imaged in a glass scintillation vial using a microPET (Siemens, Munich, Germany) small animal PET scanner. The signal was corrected for abundant cascade gamma-radiation from 52Mn that could cause random false coincidence events to be detected, and then the image was reconstructed by filtered back-projection. Additionally, we have used the digested target to spike non-radioactive Mn(II)Cl2 solutions for simultaneous PET/MR phantom imaging using a Biograph mMR (Siemens) clinical scanner. The phantom consisted of a 4×4 matrix of 15 mL conical tubes containing 10 mL each of 0, 0.5, 1.0, and 2.0 mM concentrations of non-radioactive Mn(II)Cl2 with 0, 7, 14, and 27 μCi (at start of PET acquisition) of 52Mn(II)Cl2 from the digested target added. The concentrations were based on previous MR studies that measured spin-lattice relaxation time (T1) versus concentration of Mn(II), and the activities were based on calculations for predicted count rate in the scanner. The PET/MR imaging consisted of a series of two-dimensional inversion-recovery turbo spin echo (2D-IR-TSE) MR sequences (TE = 12 ms; TR = 3,000 ms) with a wide range of inversion times (TI) from 23–2,930 ms with real-component acquisition, as well as a 30 min. list-mode PET acquisition that was reconstructed as one static frame by 3-D ordered subset expectation maximization (3D-OSEM). Attenuation correction was performed based on a two-point Dixon (2PD) MR sequence. The DICOM image files were loaded, co-registered, and windowed using the Inveon Research Workplace software (Siemens).